Overlay pieces
are made of two layers of sterling silver. The top layer has a cutout design.
The solid bottom layer (background to the cutout) is usually accented for contrast.
The Navajo silversmiths oxidize the bottom layer which darkens it. Hopi silversmiths
oxidize and etch the background (texturize it) with hashmarks. The cutout top
layer is placed over the bottom layer and the two pieces are "sweated"
together, that is, heated so that they become one. This is a very difficult skill
to master.